OB Sperryments

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Ali Tait
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#1 OB Sperryments

Post by Ali Tait »

Have lashed these up for a listen, first impressions are good. Altec Lansing 806-8a with Isophon DKT horn tweeter. Great match with the OTL, being around 104db or so-

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#2 Re: OB Sperryments

Post by Ali Tait »

Still running actively, running the Eminence up to 700hz, then over to the AL's from there up to 7k, tweeter takes over after that.

Not supposed to run the AL's under 800, but I reckon it should be fine as I'm using an 8th order slope.
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#3 Re: OB Sperryments

Post by Mike H »

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Watching.



That is a very busy room! Fab reel-to-reel too.
 
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#4 Re: OB Sperryments

Post by pre65 »

Are you still thinking of using the Alpair 12P Ali ?
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#5 Re: OB Sperryments

Post by cressy »

Love the books, paradise lost and dune series :D

Something sadly lacking from alot of homes these days.
Mate of mine hasnt a single book in the house :shock:
Asked him why once, his reply, if i want to know things I just use my phone......
Dont think he got the point
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#6 Re: OB Sperryments

Post by Dave the bass »

Is it true that all of Ali's books are unreadable by the English cos they're written in Scotterish?

heheheheheheheheh (etc).
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#7 Re: OB Sperryments

Post by chris661 »

Ali,
Looks like a nice setup.
You might find an improvement if you put some polyester wadding around the horn. Couple of reasons:
- Metal horns tend to ring a little, this would help damp it out. The ones in my PA system ring like a bell around 900Hz, but that disappears when you bolt them down.
- Diffraction from the sharp horn edge will colour the off-axis sounds a lot, and likely produce a little bit of ripple on-axis, too. You're likely to get a smoother sound.

I wouldn't worry too much about running the horn quite low. If you've got titanium diaphrams, they give you lots of warning (hammering on the phase plug) before giving up. Aluminium ones, not so much. Still, they're intended for fairly high volumes. Keep an eye on the volume, and maybe try 4th order down to 500Hz or so. IIRC 8th order actually loses a little power handling, because you've got more output around the knee of the crossover. 4th order doesn't have quite as much at the knee, and still cuts below the crossover point steeply enough to keep things safe.

If it's sounding good now, though, I'd just kick back and enjoy the music.

Chris
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#8 Re: OB Sperryments

Post by Ali Tait »

pre65 wrote: Tue Feb 28, 2017 12:13 pm Are you still thinking of using the Alpair 12P Ali ?
Not at the moment Phil, though I might use it to fill in 200-700. Need a bigger baffle though!
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#9 Re: OB Sperryments

Post by Ali Tait »

Dave the bass wrote: Tue Feb 28, 2017 12:30 pm Is it true that all of Ali's books are unreadable by the English cos they're written in Scotterish?

heheheheheheheheh (etc).
Awanboilyerheidyesoftsouthernjessie. :D
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Ali Tait
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#10 Re: OB Sperryments

Post by Ali Tait »

chris661 wrote: Tue Feb 28, 2017 1:00 pm Ali,
Looks like a nice setup.
You might find an improvement if you put some polyester wadding around the horn. Couple of reasons:
- Metal horns tend to ring a little, this would help damp it out. The ones in my PA system ring like a bell around 900Hz, but that disappears when you bolt them down.
- Diffraction from the sharp horn edge will colour the off-axis sounds a lot, and likely produce a little bit of ripple on-axis, too. You're likely to get a smoother sound.

I wouldn't worry too much about running the horn quite low. If you've got titanium diaphrams, they give you lots of warning (hammering on the phase plug) before giving up. Aluminium ones, not so much. Still, they're intended for fairly high volumes. Keep an eye on the volume, and maybe try 4th order down to 500Hz or so. IIRC 8th order actually loses a little power handling, because you've got more output around the knee of the crossover. 4th order doesn't have quite as much at the knee, and still cuts below the crossover point steeply enough to keep things safe.

If it's sounding good now, though, I'd just kick back and enjoy the music.

Chris
Just a lashup at the moment Chris. If I like it enough they will be mounted where the B200's are now. They are Ali diaphragms, and from reading on an Altec forum, you do need to be careful driving them too low. Altec themselves changed from 500hz to 800, I assume because they were getting too many back for repair. :-)

I'll give 4th order a go, I seem to prefer the steeper slopes though subjectively.
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#11 Re: OB Sperryments

Post by chris661 »

Yep, definitely be careful with ally diaphragms. I use titanium in the PA system for a little mechanical safety. Aluminium is better damped at the top end, though.

Chris
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#12 Re: OB Sperryments

Post by IslandPink »

Interesting stuff. What's the 8" midrange ?
Ali Tait wrote: Tue Feb 28, 2017 2:22 pm They are Ali diaphragms, and from reading on an Altec forum, you do need to be careful driving them too low. Altec themselves changed from 500hz to 800, I assume because they were getting too many back for repair. :-)

I'll give 4th order a go, I seem to prefer the steeper slopes though subjectively.
Would it be too subversive to comment that I've happily run the 288H's on Azuras or Yuichis with a first-order high pass or no filter for years ? :D
I once took the back off one of the 288H's while it was playing fairly loud, with no crossover. The only way I could tell the diaphragm was moving was by feeling it with my fingers.
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#13 Re: OB Sperryments

Post by Ali Tait »

It's a Visaton B200 Mark, what was originally used from 200hz up. Not in use at the moment.

Don't think these would be as robust as yours!

Been looking at the Great Plains Audio website, they sell modern versions of these drivers, might get a pair as I don't know the provenance of the Altecs or when or indeed if the diaphragms have ever been changed.
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#14 Re: OB Sperryments

Post by IslandPink »

They may not need changing if they haven't been abused. Whether the GPA ones would sound the same is not certain.
So which bits do you run with DSP ? - hopefully not the bit driven by the OTL ?
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#15 Re: OB Sperryments

Post by Ali Tait »

The DSP is only used for the crossover, I don't mess with the frequency response otherwise. The bass is run with a Behringer Inuke 3000w class D amp feeding the Eminences, which run up to 700hz. The Altecs run 700 to 7k, which are fed by the OTL. 7k up is the Isophons, currently run with a Temple Audio Bantam Gold class D jobbie, mostly because it's small and can be tucked behind the OTL. :D

I have an EL34 SEP amp which I'll try on the treble when I get time at the weekend.

Hear you about the GPA drivers. The Altecs sound good, but having never heard any others, I've no yardstick to judge them by. Suspect the diapragms may have been changed in the past though, as the connecting wires are terminated with plastic bodied crimps, which I don't think would be original.
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